Manufacture of zinc oxide



Patented Dec. 19, 1933 UNITED STATES PATENT OFFICE 1,940,125 V MANUFACTURE OF ZINC OXIDE Application June 20, 1929. Serial No. 372,264

11 Claims. (Cl. 23-148) This invention relates to the manufacture of zinc oxide and has for its object the provision of improvements in the method of and apparatus for manufacturing zinc oxide. The invention 6 relates more particularly to the prevention of the formation of incrustations of zinc oxide and the like often referred to as rock-oxide; and to the prevention of the loss of appreciable quantities of merchantable zinc oxide by adhesion to coarse particles and accretions of non-merchantable material, in the manufacture, of zinc oxide.

In the manufacture of zinc oxide according to the zinc retort volatilization (French) process, a charge of zinc metal is heated until a stream of zinc vapor issues from an orifice or opening in the retort, provided for this purpose. The retort is generally heated externally with hot combustion gases. The stream of zinc vapor passes into an oxidizing environment and burns to zinc oxide pigment in a lazy-flame characteristic of .this particular process. According to usual practice, an upright elongated box-like compartment surrounds the mouth or exit of the retort. Thebox extends to the floor level below and has a flue opening at the top leading to collecting chambers for the settling'out of zinc oxide. An opening is provided at or near the bottom of the compartment for the introduction of surrounding air. Since a suction draft is applied to the system, air is drawn into the compartment and supplies the necessary oxidizing environment. This air also transports the lighter zinc oxide particles to the collecting chambers. Some of the heavier zinc oxide particles or agglomerates fall to the bottom of the oxidizing chamber.

While a very high grade zinc oxide pigment may be manufactured by the retort volatilization process, various production difliculties are encountered. As the zinc vapor issues from the orifice or 40 exit of the retort, an incrustation of zinc oxide and metallic zinc forms around and in due time partly or entirely closes the discharge end of the retort. This material is often called horns. Rock-oxide also forms on, attaches to and builds up on the front and sidewalls of the oxidizing chamber and fines leading to the collecting chambers. During the zinc volatilization process, molten zinc'is splashed out of the retort when a violent ebullition of the zinc takes place. A part of this molten zinc is frequently condensed on the homs, while some of it is also carried over onto the side walls or falls to the bottom of the oxidizing chamber. 7

An efiort is periodically made to clean the horns" from the mouth of the retort and to remove the incrustations of rock-oxide from the side walls of the oxidizing chamber, in order to aid the zinc oxide making process and to recover the zinc values present in these accretions. To this end the material is scraped loose and dropped to 60 the bottom of the oxidizing chamber, where it is collected. A door is usually provided for this purpose in the chamber wall in front of the orifice of the retort, opening into the bottom of the oxidizing chamber. The collected by-product is often referred to as drop-oxide, which term will hereinafter be employed generically for such zinc products as attach themselves to the oxide-making apparatus. The weight of the drop-oxide often runs in excess of 8% of the weight of zinc charged to the retorts. It is removed from the bottom of the chamber, and is subsequently subjected to a treatment operation for the recovery of its zinc content.

In the practice of the present invention the formation of drop-oxide in the manufacture of zinc oxide may be materially reduced. The amount of drop-oxide formed may be reduced as much as '75%. This reduction in amount of drop-oxide formed, moreover, does not impair v the chemical and physical properties of the zinc oxide collected under the new conditions of operation. Important economies may therefore be effected in the practice of the invention.

According to the present invention, a protec- 85, tive layer or film of air is interposed between the stream of zinc vapor and the side walls of an oxidizing chamber or flue into which the vapor is introduced. The invention also contemplates the introduction of the stream of zinc vapor into the oxidizing chamber in such man nerthat it will move centrally thereof, and be kept out of contact with the front and side walls of the chamber.

These and other features of the present inven- 9i tion will perhaps be best understood by referring V to the accompanying drawings, taken in conjunction with the following description, in which:

Fig. 1 is an end elevation in section of an apparatus adapted for the practice of the present invention;

Fig. 2 is a horizontal section on the line 2-2 of Fig. 1; and

Fig. 3 is a part side elevation in section on the line 33 of Fig. 2.

, Referring more particularly to Fig. 1, a furnace, structure 10 resting on an elevated foundation structure 11 is provided with a horizontally disposed and arched heating chamber 12,'s urmounted by an arch 13, through which extend a plu- 110 rality of laterally disposed and spaced zinc volatilizing retorts 14. The spent combustion gases from the heating chamber pass to heat regenerators (not shown) located below the operating floor within the foundation structure 11.

The heating chamber is provided with side walls 15 and 16, built of suitable heat-refractory brick. The whole furnace structure is tied in by a plurality of spaced and vertically disposed support members 17, such as railway rails, the upper ends of which are held in position by means of adjustable tie rods 18. a

The retorts are provided at one end with charging sleeve 19 for the introduction of zinc metal. A removable plug or stopper 20 fits into the sleeve. Mud is advantageously plastered over the end of the retort to make the sleeve and plug vapor tight. The other end of the retort is provided with an orifice 21 for the escape of vola-' tilized zinc. In the preferred practice of the invention, a nozzle extension or nipple 22 fits into the orifice.

An upright elongated or box-like structure 23 rests against or is built into one side of the furnace structure. The walls of the structure define oxidizing chambers 24, into which the vola'tilized zinc vapor may be conducted. This boxlike compartment preferably extends from the bottom of the furnace structure to the top thereof. It is provided with an opening or openings 25 at or near the bottom thereof for the introduction of atmospheric air into the chamber for oxidizing purposes. The top of the box-like structure is provided with a flue or offtake 26 .for the withdrawal of zinc oxide. The outer face of the box-like structure, directly opposite the vapor exit of the retorts, is provided with a hinged metallic door or doors 27.

In the furnace illustrated, referring more par- -.ticularly to Figs. 2 and 3, it will be noted that the furnace structure contains a plurality of zinc volatilizing retorts arranged in pairs. The orifices or exits of each pair of retorts lead into a single oxidizing chamber, made possible by a M plurality of spaced upright walls 28 built into or against the furnace structure. These walls are preferably constructed of heat-refractory brick.

A compressed air feed line 29 is located adjacent to the outer wall of the box-like com- U partment, horizontally of the furnace illustrated.

It is provided with valved off-take pipes 30 that connect with perforated pipes 31 extending along the faces of the separating walls. In the preferred practice of the invention, the perforated pipes are located slightly below the orifices of the retorts. The pipes and perforations are so arranged that a film or layer of air may be provided along the faces of the oxidizing chamber walls. As shown in Fig. 2, the perforated pipes may be arranged in various positions. In one compartment are shown perforated pipes along two side walls, whereas in the other compartment are shown perforated pipes along all four of its side walls. Any desirable combination may 6 be employed in the practice of the invention.

In the practice of the invention, the above described apparatus may be operated as follows:

The plugs 20 are removed from the sleeves 19 and a charge of zinc metal, in either solid and/or liquid form, is introduced into the retorts 14. The plugs are then replaced and luted tight. Hot combustion gases from a suitable source, such as from the combustion of such fuelas coal, gas,

oil and the like, are introduced into the heating chamber 12. The hot gases circulate in and among the retorts and ultimately find their way to the heat regenerators (not shown) located below the operating floor within the foundation structure 11.

When the retorts 14 have been sufliciently heat-- ed to bring the zinc metal confined therein to a boiling temperature, an ebullition of zinc vapor takes place. The rising zinc vapor escapes through the orifices 21, and through the extension nozzlesor nipples 22, in case they are employed, into the oxidizing chambers 24. The air coming through the openings 25 meets the zinc vapor, upon which a burning of the zinc to zinc oxide takes place. A sufliciently strong draft of air passes'upwardly through the oxidizing chambers 24 to carry the lighter zinc oxide particles through the fines 26 to the collecting chambers (not shown).

In the heretofore customary practice of making zinc oxide in this type of apparatus, the zinc vapor passing through the orifices 21 impinges against and adheres to'the front and side walls of the chambers 24. Certain portions of the newly formed zinc oxide also contact with and adhere or fuse to the walls of the oxidizing chamber. Some of the heavier particles or agglomerates fall to the bottom of the chamber, and are with drawn through the openings 25 together with such other zinc materials as are scraped from the chamber walls and retort orifices.

In the practice of the present invention, compressed air is passed into the main feed line 29. Regulated amounts of the air are withdrawn through the pipes 30 and 31 to offset or in large part inhibit the formation of drop-oxide. The air rising through the holes in the tops of the perforated pipes tends to form a film, layer or blanket of air along the faces of the oxidizing chamber walls. In this manner, the zinc vapor and the newly formed zinc oxide are for the most part kept out of contact with the walls of the oxidizing chamber.

If the extension nozzles or nipples 22 are of suitable length, the volatilized zinc vapor may be made to enter the combustion chamber substantially centrally thereof. The film or layer of air, moving in the same direction as the rising zinc vapor and newly formed zinc oxide, serves to keep the vapor and oxidized products out of contact with the chamber walls. The jets of compressed air likewise carry into the collecting system much'marketable zinc oxide that would otherwise fall into the drop-oxide chamber. The eddies of air produced by the air jets also tend to prevent the zinc oxide from forming loose agglomerates of so-called philosophers wool, which are too'heavy to be carried into the collecting system and likewise fall down with the drop-oxide.

While the specific application of the invention given above has been confined for the most part to the so-called French process of manufacturing zinc oxide, the invention may also be otherwise applied. Thus, the process and apparatus of the invention may be adapted to the manufacture of zinc oxide according to the so-called American process, 1. e., by the reduction of zinc ores and the liberation of zinc vapor, which is burned ried on in an oxidizing atmosphere provided within a walled enclosure outside of the reduction (distillation) furnace. In this case, a layer or film of air is advantageously interposed between the stream of zinc vapor and gas (fume) leaving the reduction furnace and the walls of the oxidation chamber.

While zinc vapor issuing from a reduction or distillation furnace may be in whole or in part burned to zinc oxide in the open atmosphere, the resulting products are conducted into and through a flue or conduit to a place for collection. Such a flue or conduit is, of course, to be regarded as an "oxidizing chamber within the purview of the present invention, since the formation of drop-oxide and the like may be to a great extent inhibited upon the inner side walls thereof in accordance with the practice of the present invention.

We claim:

1. The method of inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process which comprises interposing a layer of air between a stream of the zinc vapor and the side walls of the oxidation chamber.

2. The method of inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process which comprises blanketing the side walls of the oxidation chamber with a layer of gas in amount adapted to prevent zinc vapor from contacting with said side walls.

3. The method of inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process which comprises introducing a stream of the zinc vapor centrally of the oxidizing chamber, and interposing a layer of air between the stream of zinc vapor and the walls of said chamber.

4. The method of inhibiting the formation of drop-oxide in the manufacture of .zinc oxide by the zinc retort volatilization process which comprises passing a plurality of streams of zinc vapor into an oxidizing chamber, and interposing a layer of moving air along the walls of the oxidizing chamber in amount adapted to keep the vapor out of contact with said walls.

5. The method of inhibiting the formation of drop-oxide in the manufacture of zinc oxide which comprises passing the volatilized products from a zinc distillation furnace to an oxidizing chamber, and interposing a layer of air adjacent the inner walls of said chamber.

6. The method of inhibiting the formation of drop-oxide in the manufacture of zinc oxide which comprises passing the volatilized products from a zinc distillation furnace to an oxidizing chamber, and interposing a layer of air adjacent the inner walls of said chamber, said layer of air moving in the direction of the volatilized products. 7

7. An apparatus for inhibiting the formation of drop-oxide in the manufacture of zinc oxide comprising a chamber for the oxidation of volatilized products from a zinc distillation furnace, an air supply conduit in association with the walls of said oxidizingchamber, said air supply conduit being adapted to spread a layer of air adjacent the inner walls of the oxidizing chamber.

8. An apparatus for inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process comprising a retort, an oxidation chamber, and a conduit associated with the oxidation chamber for spreading a layer of air along the inner face of the side walls thereof.

9. An apparatus for inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process comprising a retort, an oxidation chamber, and a perforated conduit adjacent the side walls of the oxidation chamber, said conduit being located at a level in respect to the orifice of the zinc retort at which a layer of air may be interposed between the walls of the chamber and a stream of zinc vapor introduced therein.

10. An apparatus for inhibiting the formation of drop-oxide in the manufacture of zinc oxide 110 by the zinc retort volatilization process comprising a retort, an oxidation chamber, and a conduit'associated with the oxidation chamber for the passage of compressed air, said conduit being perforated at its top for the escape of air 5 and adapted to spread a layer of air along the inner walls of said chamber.

11. An apparatus for inhibiting the formation of drop-oxide in the manufacture of zinc oxide by the zinc retort volatilization process com- 2 prising a retort, an oxidation chamber, and an extension nozzle at the orifice of the retort, said nozzle extending centrally of the oxidation chamber, and means associated with the chamber for spreading a layer of air along the inner walls 125 thereof.

WILLIAM A. HANDWERK. WENDEL REISER. 

